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Horner’s Syndrome: Signs, Causes & Treatment

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Also called oculosympathetic palsy or Bernard-Horner syndrome, Horner’s syndrome is a relatively rare disorder characterized by drooping of the eyelid (ptosis), a constricted pupil (myosis), and absence of sweat on the face (anhidrosis). 

It can be congenital (present at birth), but it is more commonly caused by something that disrupts one of the three sympathetic nervous system pathways that serve the eyes. This can range from blunt force trauma to an illness or snake bite. 

Treatment typically involves managing the cause of Horner’s syndrome.


Horner’s syndrome is considered rare. It only impacts about 1 out of every 6,000 people and can occur in people of all ages, genders, and ethnic groups. 

The syndrome is caused by a disruption in the nerve pathways that serve the eyes. This is part of the sympathetic nervous system, which controls automatic functions that help your brain tell your eyes how to react to stimuli to function in different situations. 

There are three main sympathetic nerve pathways that serve the eyes, and disruption of any of these can cause Horner’s syndrome. 

Central (or First-Order) Horner’s Syndrome

The first stage of the nerve pathway leads from the hypothalamus in the brain down through the brainstem and spinal cord and into the chest. First-order Horner’s syndrome is a disruption in this nerve pathway.

Preganglionic (or Second-Order) Horner’s Syndrome

The second stage of the nerve pathway starts at the chest and travels to the top of the lungs and along the carotid artery in the neck. Second-order Horner’s syndrome is a disruption in this pathway.

Postganglionic (or Third-Order) Horner’s Syndrome

The third stage of the nerve pathway travels from the neck to the eye and middle ear. Disruptions in this pathway can cause third-order Horner’s syndrome.

Symptoms of Horner’s Syndrome

Typically, Horner’s syndrome will only affect one side of the face — the same side of the face that the disrupted nerve pathway is on. Symptoms can include the following:

  • Miosis, which is a small or constricted pupil
  • Ptosis, which is a drooping of the upper eyelid
  • Enophthalmos, which is sinking of the eye into the eye socket)
  • Anhidrosis, which is a lack of sweating on the affected side of the face that is sometimes accompanied by flushing with physical exertion or emotional reactions
  • Anisocoria, which is a noticeable difference between pupil sizes in the two eyes
  • Delayed or little dilation of affected pupil in dim lighting
  • A slightly elevated lower lid
  • Lighter iris color in the affected eye in children under the age of 1 

Most of the time, the symptoms of Horner’s syndrome are mild and often not very noticeable. They can often even be hard to detect and diagnose. 

Frequently, they do not interfere much with a person’s vision or health. However, Horner’s syndrome can be an indicator of a more serious issue or condition that requires attention.

Risk Factors

Typically, Horner’s syndrome is caused by something that interferes with one of the three sympathetic nerve pathways supporting the eye. This can include an accident, injury, trauma, insect or snake bite, illness, or certain cancers. 

More rarely, it can be congenital. This means you are born with it. Horner’s disease can be genetically passed down through families, so having a family member with the condition can increase the likelihood of having it as well.

Causes  of Horner’s Syndrome

Most of the time, Horner’s syndrome is caused by something that damages one of the sympathetic nerve pathways supporting the eye. The sympathetic nervous system helps to automatically regulate autonomic functions of the body based on a response to the environment. This includes factors involved in the “fight-or-flight” response, such as blood pressure, heart rate, perspiration, and pupil size. 

The cause of Horner’s syndrome often depends on which of the three sympathetic nervous system pathways are disrupted. 

Disruption of First-Order Neurons

Anything that damages the hypothalamus, spinal cord, or brainstem, causing lesions in these regions, can cause a disruption of first-order neurons and first-order Horner’s syndrome. This typically includes intracranial conditions, such as these:

  • Intracranial tumors
  • Spinal cord tumors
  • Stroke
  • Spinal trauma above T-2 or T-3
  • Multiple sclerosis or other diseases that cause demyelination (loss of protective sheath on neurons)
  • Trauma to the neck
  • Syringomyelia (cyst in the spinal column)
  • Neoplasms like glioma

Disruption of Second-Order Neurons

Damage to the upper part of the chest into the side of the neck can cause second-order Horner’s syndrome. This can be the result of any of the following:

  • Trauma to the chest cavity or cervical rib
  • Surgery in the chest cavity
  • Schwannoma (tumor of the myelin sheath)
  • Lung cancer
  • Damage to the aorta (blood vessel traveling from the heart)
  • Spinal cord trauma
  • Thyroid malignancies
  • Subclavian artery aneurysm 

Disruption of Third-Order Neurons

Third-order Horner’s syndrome can be caused by damage to the side of the neck and into the muscles of the iris and facial skin. This can be caused by the following:

  • Trauma to the jugular vein or carotid artery on the side of the neck
  • Migraines
  • Cluster headaches
  • Tumor at the base of the skull
  • Infection near the base of the skull
  • Carotid artery dissection, thrombosis, or aneurysm

Horner’s Syndrome in Children

Horner’s syndrome can be congenital and present at birth, but the most common causes in children include the following:

  • Injury during delivery to the neck or shoulders
  • Neuroblastoma (tumor of nervous and hormonal system)
  • Defect in the aorta that is present at birth

Unknown Causes

In about 35 to 40 percent of cases, the cause of Horner’s syndrome is unknown. This is often called idiopathic Horner syndrome.


Horner’s syndrome is often not very noticeable and commonly goes undetected. There are several methods for diagnosing the disorder even with mild symptoms. 

Horner’s syndrome is often caused by an underlying condition, and diagnosis will help to determine treatment options.

Medical Examination

Commonly the first step in diagnosing Horner’s syndrome is a medical examination that will include a full assessment of your medical history and evaluation of all symptoms. This can be done by your primary care physical (PCP) who can then refer you to the necessary specialist when needed.

Eye Exam

An eye exam by an eye doctor, such as an ophthalmologist, can result in a diagnosis of Horner’s syndrome. The eye doctor will place a medicated eye drop into your eye and examine the way your pupils react to the medication. The test is often repeated again in 48 hours. 

The eye drop test can help to diagnose the condition and indicate where the issue is.


Aside from an eye drop test, imaging tests are often done as well to locate the specific area where the disruption to the nerve pathway is causing Horner’s syndrome. This can include the following:

  • MRI (magnetic resonance imaging)
  • CT (computerized tomography)
  • Chest x-ray
  • MRA (magnetic resonance angiography)
  • Ultrasonography of the carotid artery


There are no specific treatments for Horner’s syndrome directly, but once the root cause of the syndrome is discovered and managed, the symptoms of Horner’s syndrome will often dissipate. 

Treatment is dependent on the cause and location of the nerve pathway disruption. This can involve surgical removal of the lesion, radiation or chemotherapy for tumors, and symptomatic and supportive care.

Both Addie syndrome and Wallenberg syndrome are rare disorders that have similar symptoms to Horner’s syndrome. They are often used for comparison and a differential diagnosis. 

Addie syndrome is a neurological disorder that affects the pupil of the eye. While the pupil is dilated (larger than normal) most of the time, , it can also be constricted as with Horner’s syndrome and have slow reaction to light as well. Poor reflexes are also often a symptom of Addie syndrome.

Caused by a blood clot, Wallenberg syndrome can show symptoms of Horner’s syndrome on the side where the lesion is present along with staggering gait, difficulty forming words, dizziness, trouble swallowing, lack of coordination, low eye pressure, rapid involuntary eye movement, and loss of sensation on the side opposite of the lesion.

Horner’s Syndrome FAQs

What are the three classic signs of Horner’s syndrome?

The three main signs of Horner’s syndrome are myosis (constricted pupil), ptosis (upper eyelid droops), and lack of sweating on the affected side of the face (anhidrosis).

What causes Horner’s syndrome?

Horner’s syndrome is usually caused by damage or disruption to the sympathetic nerve pathways that serve the eye, which can include trauma or medical conditions. It can more rarely be congenital.

Is Horner’s syndrome life-threatening?

Horner’s syndrome is typically mild and does not often impair your physical health or vision dramatically. It can, however, be indicative of an underlying and serious medical condition that can be life-threatening.


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  2. Horner’s Syndrome. National Organization for Rare Disorders Rare Diseases Database.
  3. Horner Syndrome. (June 2022). American Academy of Ophthalmology.
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  5. Horner Syndrome: Clinical Perspectives. (April 2015). Eye Brain.
  6. Causes of Horner Syndrome: A Study of 318 Patients. (September 2020). Journal of Neuro-Ophthalmology.
  7. Horner Syndrome: A Clinical Review. (December 2017). ACS Chemical Neuroscience.

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